MINORITY-CARRIER RECOMBINATION KINETICS AND TRANSPORT IN SURFACE-FREE GAAS/ALXGA1-XAS DOUBLE HETEROSTRUCTURES

We have measured room-temperature band-to-band recombination decay kinetics in superior quality GaAs heterostructures, and have observed the longest lifetime (2.5 mus) observed for any GaAs/AlxGa1-xAs structure to date. Additionally, using a novel time-resolved optical photoluminescence imagining technique, analogous to the Haynes-Shockley experiment, we have also measured room-temperature minority-carrier transport in this series of ''surface-free'' GaAs/Al0.3Ga0.7As double heterostructures, measurements only possible in high-quality samples with long lifetimes and intense photoluminescence. We find the transport to be diffusive with diffusion lengths of greater than or similar to 100 mum. Further, we find, for thick structures, minority-carrier transport is hole-dominated ambipolar diffusion, as expected for high-purity n-type material. However, for thinner structures, we find that the minority-carrier transport is time dependent, changing from ambipolar diffusion at early times, as in thick structures, to electron-dominated diffusion at later times. We show that these structures become effectively p-type modulation doped due to the relative ''impurity'' and thickness of the AlxGa1-xAs compared to the GaAs. As a result, the minority-carrier species changes from holes to electrons for decreasing GaAs layer thicknesses. Cumulatively, we show the band-to-band recombination decay kinetics and carrier transport results to be in excellent qualitative and quantitative agreement. Moreover, our results are in excellent agreement with electrical transport measurements of electron and hole mobilities. Finally, with our measured room-temperature lifetimes and minority-carrier transport measurements versus GaAs layer thickness, we accurately calculate the interface recombination velocity for these structures, with the result S is similar to 40 cm/s, among the lowest ever reported for any GaAs/AlxGa1-xAs structure.